Amphoteric copolymer derived from vinylpyridine and acetoxystyrene

ABSTRACT

A unique polymer was synthesized via copolymerization of vinylpyridine and acetoxystyrene under radical-initiated conditions followed by acidic or basic hydrolysis of the acetoxy group to afford the corresponding hydroxy group. The built-in acid-base dual functionality (phenolic and pyridyl units) in this polymer backbone gives rise to its unique solubility properties over a wide pH range in both aqueous and non-aqueous media. Due to its amphoteric nature, this polymer finds application as an anti-stat, viscosity modifier, and/or ion-exchange resin.

BACKGROUND OF THE INVENTION

This invention relates to a new copolymer derived from acetoxystyreneand vinylpyridine.

Various copolymers of p-acetoxystyrene and other polymerizable monomersare known in the art and have miscellaneous end uses. For example,Japanese Kokai Nos. 77 35779, published Mar. 18, 1977, and 77 58087,published May 13, 1977, disclose copolymers of p-acetoxystyrene anddivinylbenzene which are hydrolyzed, treated with paraformaldehyde anddimethyl amine or pyrolidine, and quaternized with methyl bromide ordimethyl sulfate to obtain anion exchange resins. Japanese Kokai No. 7735189, published Mar. 17, 1977, teaches the sulfonation of copolymers ofp-acetoxystyrene and a polyene compound such as divinylbenzene to obtainmicroporous cation exchange resins. Arshady et al., "Phenolic Resins forSolid-Phase Peptide Synthesis: Copolymerization of Styrene andp-Acetoxystyrene", J. Polymer Science: Polymer Chemistry Edition, Vol.12, 2017-2025 (1974), show copolymers of styrene, p-acetoxystyrene, anddivinyl benzene used to produce cross-linked resins for solid phasepeptide synthesis.

In addition to the foregoing, the prior art also shows differentpolymers of p-vinylphenol for various applications. Thus, JapanesePatent Publication No. 34902/1978 teaches compositions comprising apolymer having more than 20 mole percent of p-hydroxystyrene (i.e.,p-vinylphenol) and an aromatic azide compound, which are useful forphotoresist, relief printing plate, and offset printing plateapplications. German Offenlegungschrift DE No. 3,311,129, published Apr.7, 1982, shows corrosion-resistant waterborne coatings useful onphosphated metals based on solutions of aminomethylatedpoly(4-vinylphenols) prepared by reacting poly(4-vinylphenol) withformaldehyde and methylhydroxyethyl amine. Furuya (Res. Inst. Polym.Text., Yatabe, Japan) Hokuku-Sen'i Kobunshi Zairyo Kenkyusho 1981,(129), 13-16 (Japan), abstracted in Chemical Abstracts 95:2205-45h,shows the reaction of poly(p-vinylphenol) and diazotized 3- or4-substituted aniline to obtain polymers which produce complexes withcopper. Such polymers would thus appear to be useful as metal chelatingagents.

Copolymers of dialkyl muconates and polymerizable co-monomers are alsoknown in the art. Thus, Bando et al., Journal of Polymer Science,Polymer Chemistry Edition, Vol. 15, 1917-1926, (1977), disclosecopolymers of diethyl muconate with styrene, acrylonitrile or2-vinylpyridine.

The prior art in U.S. Pat. No. 4,775,730 also discloses copolymers ofacetoxystyrene and a polyunsaturated carboxylic ester.

However, none of the prior art disclosed above provides a suitablepolymeric material which has unique solubility properties over a wide pHrange in both aqueous and non-aqueous media.

DESCRIPTION OF THE INVENTION

In accordance with this invention, a new class of resin is providedwhich is an amphoteric copolymer derived from vinylpyridine andacetoxystyrene. This new polymer is prepared according to the followingscheme: ##STR1##

where n is from about four (4) to about 20,000 and M is lithium, sodium,or potassium.

This unique copolymer is present in different amphoteric forms withintermolecular and intramolecular H⁺ transfer as shown below: ##STR2##

In formulae 3 and 4 above, n is four (4) to 20,000, and these areclassified as the intermolecular and intramolecular equivalents thereof,(i.e., of formula 2).

It has been found that this copolymer which consists of repeating basic(e.g., pyridyl) and acidic (e.g., phenolic) monomer units imparts uniquephysicochemical properties to the polymeric backbone.

The copolymer of this invention may be suitably prepared by the freeradical polymerization of vinylpyridine and acetoxystyrene, in solution,emulsion, or suspension, using well-known polymerization techniques. Afree radical type of polymerization initiator or "catalyst" is generallyemployed which is preferably an azo compound such as2,2'-azobis(2,4-dimethylpentanenitrile)(sold by duPont as "VAZO-52"),2,2'-azobis(2methylpropanenitrite)(sold by duPont as VAZA-64),2,2'-azobis(methylbutyronitrile), (sold by duPont as "VAZO-67") and1,1'-azobis(cyanocyclohexane)(sold by duPont as "VAZO-88"). Otherfree-radical polymerization initiators which may be used are peroxycompounds, e.g., benzoyl peroxide and potassium persulfate, andperesters and peroxyketals sold by Pennwalt under the trademark"Lupersols".

The polymerization is generally carried out at a temperature suitable topromote the reaction, preferably from about 50° C. to about 100° C. andmore preferably from about 60° C. to about 80° C. During thepolymerization, it also preferred to employ an organic solvent tofacilitate ease of reaction. Such solvents include soluble alcohols, di-or tri-functional alcohols, ketones, cyclic ethers, and mixturesthereof. Especially preferred solvents are aliphated alcohols havingabout one (1) to about four (4) carbon atoms, such as methanol, ethanol,n-propanol, isopropanol, and 1,2-propane diol. Most preferred ismethanol and ethanol.

The conversion of the copolymer (formula 1) to the formula 2 copolymeris carried out by acid or base catalyzed alcoholysis wherein thepreferred alcohols are methanol or ethanol. The acid catalyzedmethanolysis, in general, is more fully described in copendingapplication Ser. No. 07/706,601 filed May 28, 1991, and which isincorporated herein by reference. However, when using HCl as the acidcatalyst, it is desirable to utilize greater amounts than that disclosedin Ser. No. 07/706,601. When using the base catalyzed methanolysisprocess, the procedure set forth in U.S. Pat. No. 5,087,772 can be used;this patent is incorporated herein by reference.

The copolymer of the invention will generally contain about one (1) toabout ninety-nine (99) weight percent of the designated vinylpyridineand about one (1) to about ninety-nine (99) weight percent of thep-acetoxystyrene monomer. However, a preferred copolymer is made fromequal molar ratios (1:1) of vinylpyridine and acetoxystyrene.

The copolymer of this invention has various applications. Thus, thecopolymer may be blended with any of various radiation polymerizablepolyunsaturated compounds, e.g., polyol acrylates or methacrylates, andoptionally a monounsaturated radiation polymerizable compound, e.g.,ethoxyethyl acrylate to form radiation curable coating compositions. Thecopolymers can also be used in the preparation of negative actingphotoresists, e.g., by dissolving the copolymer in an organic solventsuch as a mixture of xylene and butyl acetate with a compound serving tocross-link the copolymer when exposed to suitable radiation, e.g.,2,6-bis(4-azidylbenzylidene)-4-methyl cyclohexanone (bis-azine). Such acomposition may be coated onto a surface subjected to suitable UVradiation to cross-link the copolymer while in contact with anappropriate photomask and the surface developed by dissolving theuncrosslinked polymer in a solvent to obtain a pattern of exposedsurface of fairly high resolution.

The amphoteric copolymer is also useful in a variety of environmentaland industrial applications, e.g., variable-charge, ion-exchangemembranes (as a function of pH) to perform demineralization,de-alkalization, and purification of waste water. It is also useful as aselective chelating agent for trace metals (Hg, Cd, Cu, and Ni) in watertreatment. This amphoteric copolymer is useful as a viscosity modifierin displacing viscous oils from underground reservoirs, in sewagetreatment, as soil conditioners, as flocculants, and in the recovery ofminerals from aqueous suspensions, where a variety of solid-liquidseparations are encountered. This polymer is also employed in shampoosand hair conditioners, as paper fortifiers, antistats, and pigmentretention aids. It is also used as a standard for isoelectric focusingof proteins, gelatin substrates of photographic film, and, in someselect cases, as controlled release of pharmaceuticals.

DESCRIPTION OF SPECIFIC EMBODIMENT

The following examples further illustrate the present invention:

EXAMPLE I

A 100 ml 3-necked round-bottomed flask equipped with a magnetic stirrer,nitrogen inlet, reflux condenser, and addition funnel was charged with4-acetoxystyrene (4.86 g, 30 mmol), 4-vinylpyridine (3.15 g, 30 mmol)and methanol (16 ml). A solution of VAZO 52 (0.24 g, dissolved in 1 mlof methanol) was added to this stirred solution. The flask was evacuatedand flushed with nitrogen three (3) times. The solution was then heatedin an oil bath so that a very gentle reflux was maintained (bathtemperature 60° C.). Three (3) additional portions of VAZO 52 (60 mgeach) were also added to the solution at one (1) hour intervals. Afterrefluxing for twenty (20) hours, complete disappearance of4-acetoxystyrene was observed as determined by high pressure liquidchromatography (HPLC). The reaction mixture was cooled to 22° C. andconcentrated HCl (3 ml) and methanol (40 ml) were added. The solutionwas refluxed for six (6) hours and then concentrated by atmosphericdistillation to a volume of approximately twenty (20) ml. The solutionwas cooled to 22° C. and neutralized by addition of aqueous ammoniumhydroxide (6N) to a pH of seven (7). The mixture was stirred at 22° C.for one (1) hour and filtered. The product cake was washed with ten (10)ml water and dried at 50° C. under house vacuum overnight, affording 5.4g (80% yield) of copolymer product.

The synthesis of the copolymer (2) (and 3, 4, and 5 above) is presentedin Scheme 1 above. 4-Acetoxystyrene and 4-vinylpyridine (1:1 molarratio) were copolymerized in methanol under radical conditions usingVAZO 52 (2,4-dimethylpentanenitrile) as a radical initiator to producethe corresponding copolymer (1) in solution. Formula 1 was isolated (viaprecipitation from water) and independently characterized by ¹³ C and ¹H NMR. Hydrolysis of the acetoxy group in the copolymer (1) wasaccomplished by transesterification in methanol/HCl-H₂ O followed byazeotropic removal of the resulting methyl acetate. The copolymer (2)was precipitated by adding the resulting methanolic solution into excessof water. The overall isolated yield of the copolymer was 80% over thetwo (2) steps. Formula 2 was characterized by ¹ H NMR, ¹³ C NMR, IR,GPC, DSC and TGA. ¹³ C NMR and IR analysis of 2 indicated completehydrolysis of the acetoxy group. The composition of the styrene andpyridine units is approximately 1:1 as evidenced by ¹³ C NMR. Thepresence of the active hydrogen was confirmed by D₂ O-exchange in the ¹H-NMR as shown by scheme 2. The ¹³ C chemical shifts of Cα and Cβ of thepyridyl unit in the copolymer (1) observed in D₆ -DMSO were δC=149.5 forCα and 122.95 for Cβ. Protonation of the pyridine unit (by addition ofHCl to the D₆ -DMSO solution) resulted in a downfield shift of Cα(δC=141.0) and upfield shift of Cβ (δC=126.5) in Formula 1a. Comparisonof the corresponding ¹³ C chemical shifts of the copolymer (2) in D₆-DMSO showed δC=148.5 for Cα and δC=123.2 for Cβ thereby indicating that2 is probably present as 2a (where the pyridyl unit remainsunprotonated) rather than as 2b, at least under the NMR condition in D₆-DMSO solution (Scheme 2). TGA and DSC analysis of the copolymerindicated good thermal stability up to 300° C. DSC also indicated theabsence of any undesirable blockiness in the polymeric backbone. The GPCanalysis indicated Mn=1572 and Mw=2813. Polydispersity of 1.78 indicatednarrow MW-range which is preferably for obtaining good mechanicalproperties. The fact that the copolymer was not a mechanical mixture oftwo homopolymeric units was also indicated by narrow dispersity range.The wet polymer was soluble in a wide variety of organic solvents, e.g.acetone, methanol, THF, and DMSO. Due to the amphoteric nature of thepolymer (phenolpyridine acid-base pair), it was also soluble in H₂ Ounder both acidic (pH=2) and basic (pH=10) conditions. ##STR3##

EXAMPLE II

In order to demonstrate the chelating utility of this copolymer, ten(10) grams of the copolymer was produced according the process describedin Example I. A 1% solution of copper sulfate (1000 ppm CuSO₄) wascombined with 100 ml of water to produce a light blue solutioncontaining copper ions. The ten (10) grams of copolymer product wasadded, with stirring, to this solution. The resultant material wasfiltered to remove the copolymer-copper complex and the filtrate, whichwas clear and colorless, and was tested for copper sulfate content. Thefiltrate analyzed less than ten (10) ppm CuSO₄.

What is claimed is:
 1. A copolymer consisting essentially of a member ofthe group consisting of the structure: ##STR4## and the intermolecularand intramolecular amphoteric equivalents thereof; where n is from about4 to about 20,000.